Experimentally testing quantum field theory methods with spinor Bose gases far from equilibrium

The information contained in quantum many-body systems grows exponentially with the number of their constituents - this prevents the exact description of dynamics on the microscopic level as this task becomes computationally intractable. In this talk I will present quantum field theory methods which provide efficient descriptions for emerging macroscopic phenomena. With these we experimentally characterize a 87Rb spinor Bose gas far from equilibrium. By employing a quantum quench we bring the system far from equilibrium and for long times after the quench we observe universal dynamics associated to the emergence of a non-thermal fixed point [1]. In this regime the correlation function of the angular orientation of the transversal spin features rescaling in time and space. The spatially resolved read-out of the complex valued transversal spin field [2] allows the extraction of one-particle irreducible correlation functions, the building blocks of the quantum effective action [3]. We find a strong suppression of the four-vertex at low momenta emerging in the highly occupied regime.

[1] Prüfer, M. et al., Nature 563, 217-220 (2018)

[2] Kunkel, P. et al., PRL 123, 063603 (2019)

[3] Prüfer, M. et al., arXiv: 1909.05120 (2019)